Present invention relates to a bituminous coating sheet material provided on one side with a heat-activatable adhesive layer that is optionally coated with a plastic film.
In particular, the invention relates to a bituminous sheet-formed coating material for the formation of a roof covering. It is known to produce roofings by using roofing felt sheets, i.e., bituminous felt lengths, which are coated with a plastic film of, e.g., polyethylene or polypropylene, having a thickness of about 10 .mu.m.
The main function of the plastic film is to prevent adjacent parts of the roofing felt sheets from sticking to each other when the sheets are stored and transported in rolls. The heating of the roofing felt sheets is typically carried out by use of propane gas burners.
When the flame, which has a typical temperature of 1000.degree.-1300.degree. C., is directed towards the plastic film-coated adhesive layer, the plastic film decomposes and burns away and the adhesive layer is activated. However, the use of such gas burners is associated with a certain fire hazard as sometimes the support or other parts of the roof construction may catch fire.
The noted flame heating is further associated with the drawback that the decomposition of the plastic film is often incomplete and therefore areas remain where the adhesive layer is covered with film residues and, as a consequence, the desired adhesion is not obtained. DK patent publication No. 150 586 B discloses a process for producing a bituminous coating on a support, provided with pressure equalization zones. In this known process a bituminous sheet material which, on the adhesive side, is provided with rows of projections of an adhesive consisting of a mixture of bitumen and a thermoplastic elastomer, is adhered to the support. These rows are typically spaced apart about 30 mm and the projections have a maximum length of 50 mm, a typical width of 15 mm and a height of 1-3 mm.
The formation of these projections on the bituminous sheet material is effected by producing initially a sand-strewn bituminous sheet material and then rolling thereon the adhesive in its melted state using a pattern embossing roll.
The known material is appropriate for the formation of a coating with pressure equalization zones, but it is unsuitable for the formation of a fully adhered coating as, although the adhesive is heated enough for the projection to spread, it is not possible to obtain a uniform adhesive layer. Moreover, the known material is associated with the drawback that it is difficult to obtain complete removal of the film described above, as a part of the film remains on top of the projections.
GB 2.146.270 A discloses a laminated roofing coating for application in a cold process and comprising a fibrous layer optionally impregnated with bitumen, a bituminous layer laminated on one side of the fibrous layer, a synthetic resin layer laminated on the bituminous layer for protection thereof, an adhesive layer partially coated on the synthetic resin layer, and a release layer laminated on the adhesive layer.
The partially covering adhesive layer may be applied the synthetic resin layer in the form of spots, lines, stripes, or bands.
FR2.544.361 A3 discloses a roofing coasting comprising a bituminous layer wherein a connected system of longitudinal and transverse grooves are formed, and a polyethylene film provided on the side of the bituminous layer comprising the groove system. The groove system serves to secure pressure equalization. The roofing coating may comprise one or more supports.
The known roofing material is manufactured by applying the plastic film onto a plane bituminous layer, and subsequently forming the grooving in both the film and the bituminous layer simultaneously. This grooving process results in a material, which is unsuitable for the formation of a fully adhered coating, since it is difficult to obtain complete removal of the film from the bituminous layer.